Photographic film contains silver halide as the light-sensitive material. Silver halide, being light sensitive, must be handled either in complete darkness, or under light of a wavelength and intensity to which the silver halide is not sensitive. The purpose of this is to prevent the grains from being rendered developable in areas other than those of the imagewise exposure. However, working either in complete darkness or under extremely subdued light is, at best, inconvenient and can pose hazards especially when chemicals, such as those needed to process photographic materials, are in use. Additionally, working under dim, often red, light can cause eye strain.
In handling any photographic material, it is, therefore, advantageous to be able to work under a light that is as bright as possible, as long as that light will not generate unwanted density on the film. The brighter light permits the material, as well as any equipment, written directions, or labels, etc., to be seen more easily. Besides brightness, it is also preferable to have the light appear as nearly white as possible, so as to diminish strain on the vision of the user which often results from working under red, yellow, or green safelight conditions.
Lamps emitting a wavelength of light which will not produce a developable image on a particular light-sensitive photographic material are called "safelights." Ordinarily, photographic film can be handled under certain safelight for a specific amount of time before image develops on the photographic material. For example, if blue light is to be used to image the film (intentional image formation), the film is commonly prepared and handled under a yellow safelight. Often, a yellow safelight is used in conjunction with a top coat layer containing a yellow filter dye. This filter dye layer acts to absorb limited amounts of blue light, further preventing the formation of unwanted images on the photographic film.
Photographic Dyes have been used to enable the handling of photographic film under safelight or to improve the sensitivity of the film:
U.S. Pat. No. 4,801,525 of Mihara et al. discloses several dyes, which may be used singly or in combination in a hydrophilic colloidal layer which, when coated over a silver halide light-sensitive material having high sensitivity to infrared light, permits handling of the light-sensitive material under various safelights. There is no disclosure, however, of the use of the green dye of the present invention, nor of the use of this green dye in combination with a yellow dye to form a dye filter layer.
U.S. Pat. Nos. 4,855,220 of Szajewski, 4,599,301 of Osashi et al., 3,990,898 of Land, and 3,672,898 of Schwan et al. disclose the use of dyes or layers of dyes for increasing image sharpness. None of these patents relate to the use of a combination of a green and a yellow dye to decrease the sensitivity of the film under white safelight.
U.S. Pat. No. 4,220,711 of Nakamura et al. discloses the use of at least one hydrophobic UV absorbing compound to prevent color staining of a film when it is exposed to light. U.S. Pat. No. 4,220,711 also discloses that the layer containing the UV absorbing compound may also contain a water soluble dye such as an oxonol dye. This patent does not, however, disclose the green and yellow dye combination of the present invention, or the use of the oxonol dyes to affect the sensitivity of silver halide to safelight.
U.S. Pat. No. 4,952,485 of Shibahara et al. discloses the use of a yellow dye as one element in achieving intensified sharpness and high sensitivity. The patent does not, however, disclose the use of the yellow dye or a combination of a yellow dye with a green dye to decrease the sensitivity of film under white safelight.
The typical films involved in the present invention are black and white sheet films and photosensitive papers used in the graphic arts, namely for making magazine and newspaper layouts. The graphic arts industry, in response to the problems created by handling film in total darkness, or, more typically, subdued red light, began introducing products which could be effectively used under yellow safelight. By using yellow safelight, the film handlers were able to work with the film and reduce any potential hazards in the film handling area. A top coat layer containing a yellow filter dye is commonly applied to the film and, in conjunction with a yellow safelight, unwanted image formation is preventable if the film is handled rapidly.
Yellow safelights, however, did not completely solve the problems confronted in the work area. Eye strain continued to be a problem experienced by those handling the film for hours at a time. Additionally, many other jobs could not be performed in the film handling area due to lack of light, for example, proofreading of layouts or handling of chemicals. This created the need for a "brighter" and more normally lighted working environment.
As the safelight environment gets brighter, greater care must be taken in the design of the film so as to prevent unwanted density formation, or "fogging," as a result of exposure to that safelight. The ideal situation, of course, would be a film which maintains a high sensitivity to the light emitted by the intended exposure source and yet has no sensitivity to the safelight.
Practically, this problem can be addressed by offering photographic materials requiring an imaging light source of significantly higher intensity and different wavelength than the safelight. For example, a metal halide lamp can be used as the imaging light source for low sensitivity films. However, these high energy light sources are costly to buy and operate, and they pose a health risk to the operators because they emit UV radiation.
Therefore, it would be desirable to have photographic materials which are sufficiently sensitive to be imaged with a light source of moderate intensity, such as the quartz lamp, but which could be used under a white safelight, or roomlight.
A detriment of white safelights, however, is that they have an emission spectrum containing a blue component to which silver halide is intrinsically highly sensitive. In order to make these "white" appearing safelights usable, it is necessary to prevent the silver halide grains from being activated by the blue wavelength portion of the safelight's emission spectrum. This then lessens the potential for the formation of unwanted density (i.e., image formation), often referred to as "safelight fog." One way of accomplishing this goal is to coat the light-sensitive silver halide layer with a highly efficient blue absorbing material.
For example, one may add large quantities of yellow filter dye to a coating over the light-sensitive material to protect the material from "white" safelight emission. However, large quantities of yellow filter dyes in the top coat significantly reduce the intensity of blue, intentional image forming light impinging upon the silver halide layer, thereby significantly slowing the photographic speed of the film.
This created a need for a film with a filter layer that would successfully prevent most of the blue light emitted by the "white" safelight from reaching the silver halide, while not slowing the speed of the film in response to image forming quartz light. This would eliminate the choice film handlers must make today between light-sensitive materials which can be handled under bright safelight but require long or high intensity exposure due to low sensitivity, or those which must be handled in subdued red or yellow light.
The preferred situation would be to have a film with a filter layer which would prevent unwanted imaging during handling by filtering the wavelengths of blue light being emitted from the safelight, while not substantially slowing the speed of the film to the intentional image forming source.
Accordingly, an object of this invention is to provide a filter layer which, when coated over a light-sensitive emulsion layer, will reduce the formation of unwanted images when exposed to "white" safelight and thereby permit handling of the photographic film under such "white" safelight.
A further object of the invention is to provide a filter layer which, when coated over a light-sensitive emulsion layer, will permit handling of the film under safelight but will not slow the speed of the film when exposed to an intentional image forming light source.